Will attempt this.
Did you make manual changes in the ISPConfig database?
Not until after the ownership change.
Trying to find somewhere to change any userid to get the site to belong to the other client.
Any hints on what posts to change?
However there's one thing other which I might think of, and that's that I upgraded mysql from 4.0 to 4.1 a couple of days ago. However that didnt affect ISPC at the time. No fault such as this.